Carbon nanotubes (CNTs) with ultrahigh thermal conductivity and very large aspect ratio have been proposed as excellent dispersions for preparing nanofluids, a new kind of thermal performance enhanced heat transfer media. In the past decade, various techniques have been developed to produce homogeneous and long-term stable CNT contained nanofluids with or without using surfactants. The thermal performances including thermal conductivity, convective heat transfer coefficient, and boiling critical heat flux have been investigated. Efforts have been taken to elucidate the heat transfer mechanism in CNT nanofluids, and theoretical models have been proposed to predict the thermal conductivity enhancement of CNT nanofluids. This article aims to address the preparation techniques and the experimental and theoretical studies on the heat transfer charicteristics of CNT nanofluids.